Orthopaedic external fixator devices are used for facilitating bone union in fractured limbs, particularly when open wounds are present. Pins, which are driven into the bone on either side of the fracture protrude through the skin and are attached to a frame outside of the body. The wounds commonly found overlying the fracture are often treated with negative pressure wound therapy (vacuum dressings). These dressings comprise a spongy material placed in the wound, covered by an occlusive adherent film dressing. Tubing placed in contact with the sponge, beneath and sealed off by the adherent film, is attached to a source of suction and suction via the tubing causes a negative pressure within the sponge. This type of negative pressure wound therapy has revolutionised the management of these open wounds as it promotes wound healing, decreases swelling and draws away excess wound exudate and associated bacteria.
Placing of the adherent film dressing over the sponge is difficult in the presence of the pins and creating an airtight seal around the base of these pins by attempting to stick the film to them often creates leaks, allowing ingress of air and thus inhibiting vacuum formation. This is due to the fact that creases in the adherent film often cause leaks by acting as micro channels through which ambient air can be drawn in underneath the film. Attempting to apply the adherent film around these pins without getting creases is near impossible.
A number of techniques have being devised in attempts to address this common problem. One method is to seal leaks with a hydrocolloid paste applied to locations of leaks. This can however be time-consuming as the doctor has to search for these leaks. Another method is to create a “mesentery”. This involves applying half of the film to the skin or foam and then running the other half up the shaft of the pin. Another film is then applied on the opposite side of the pin, to the skin and pin, mirroring the first film, in so doing sandwiching the pin between the two adherent sides of the films and thereby creating a seal around the pin. This technique holds the disadvantages that it is very time-consuming, particularly as there are multiple pins to which such mesenteries need to be applied and the overlying structures of the external fixators restrict access to the wounds and thus makes the application of these mesenteries very difficult. This technique also increases the quantities of adherent film required for these types of dressings. This technique is further not infallible and may also leak if there are creases in the film or if two pins are place close to each another, causing a tendency of the two adherent films to separate from each other between the two pins, since attempts to avoid the formation of creases tend to keep the films in planar conditions and not to allow them to penetrate between the pins. Often the threaded part of the screw protrudes a fair distance outside the flesh entry site and it can be difficult to apply the adherent film to this threaded part in a sealing manner, with the result that leaks at these sites are more likely.
In order to increase the adhesion of the film to the skin and the base of the pin and thus to create a good seal and reduce the likelihood of a leak, the use of any materials that could reduce adhesion is typically avoided. However, this also rules out the use of antibacterial dressings and ointments around the base of a pin prior to applying the film and the potential risk of infection at the point of entry of the pin in the skin is greatly increased. This complication is relatively common even in the presence of antibacterial agents, with literature quoting figures between 10 and 50% depending on the definition of “infection”. The presence of the adherent film around the pin sites creates a moist environment, ideal for bacterial proliferation. This, combined with the fact that no antibacterial dressings are used, implies that pin site infection rates in these dressings are likely to be even higher. Depending on the severity of the infection, these patients may require more frequent hospital attendances and dressing changes, antibiotics or even removal of the pins prior to bone union taking place. Should the infection spread to the bone, the resulting osteomyelitis could further complicate the patient's recovery.
Devices have been developed which help to secure antibacterial dressings around the pin entry site, but these are not compatible with vacuum dressings as they make the possibility of creating a seal around the pins even more difficult. Other products have been described which envelope the pins in a sheath-like manner and are impregnated with antibacterial substances. However, these products also do not facilitate the possibility of creating a seal around the pins when used with vacuum dressings.
The present invention seeks to provide improved application of negative pressure wound therapy dressings in the presence of orthopaedic pins, which inhibits the disadvantages of existing techniques and apparatus as described above. In particular, the invention seeks to provide reliable and convenient sealing of the dressings and to allow for the use of antibacterial dressings around the bases of the pins.